1. Field of the Invention
The present invention relates to an image reading apparatus adapted for use in reading images.
2. Description of Related Art
FIG. 20 shows the arrangement of a film scanner as an example of conventional image reading apparatuses.
Referring to FIG. 20, an illuminating light source 2801 is arranged to illuminate a film. A film holder 2802 is arranged to hold the film and to be movable in the direction of an arrow A as viewed in FIG. 20. Light emitted from the illuminating light source 2801 passes through the film. An image forming lens 2803 is arranged to form an image of the light having passed through the film on a CCD linear image sensor 2804 (hereinafter referred to simply as the CCD).
The CCD 2804 is disposed such that its longitudinal direction coincides with a direction Z shown in FIG. 20. Accordingly, because of the positional relation between the film holder 2802 and the CCD 2804, a horizontal scanning direction, which is the longitudinal direction of the CCD 2804, is perpendicular to a vertical scanning direction, which is the moving direction of the film holder 2802. In adjusting focus, while the image forming lens 2803 (optical system) is kept stationary, the film holder 2802 holding the film original and a moving mechanism arranged to move the film holder 2802 including a shaft, etc., are moved in the direction of an optical axis (in the direction of an arrow B) by means of a focus adjusting motor (not shown), so that an in-focus state on the film is obtained.
An analog image processing circuit 2805 is arranged to perform gain setting and clamp processing actions on an analog image signal outputted from the CCD 2804. An A/D converter 2806 is arranged to convert the analog signal into a digital signal. A digital image processing circuit 2807 processes the digital image signal and is provided with a gate array for processing a CCD driving pulse signal, etc. The digital image processing circuit 2807 is thus arranged to be capable of carrying out various processes at a high speed. A line buffer 2808 is arranged to temporarily store image data. An interface part 2809 is provided for communication with an external apparatus 2810 which is, for example, a personal computer or the like.
A system controller 2811 is arranged to store a sequence of actions of the whole film scanner and to cause various actions to be carried out in accordance with commands coming from the external apparatus 2810. A CPU bus 2812 is arranged to connect the system controller 2811 to the digital image processing circuit 2807, the line buffer 2808 and the interface part 2809. The CPU bus 2812 is composed of an address bus and a data bus.
A vertical-scanning motor 2813 is provided for moving the film holder 2802 in the vertical scanning direction, i.e., in the direction of the arrow A. A stepping motor is employed as the vertical-scanning motor 2813. A vertical-scanning motor driver 2814 is arranged to drive the vertical-scanning motor 2813 according to an instruction coming from the system controller 2811. A vertical-scanning position detecting part 2815 is arranged to detect the datum position of the vertical scanning by detecting a projection of the film holder 2802 by means of a photo-interrupter. A light source lighting circuit 2816 is arranged to turn on the illuminating light source 2801.
In the arrangement described above, the film scanner is arranged to output image data to the external apparatus 2810 through the communication of a software included in the system controller 2811 (hereinafter referred to as the firmware) with a software for operating the film scanner from the external apparatus 2810 such as a personal computer (hereinafter referred to as the driver software).
The procedures for operating the film scanner are next briefly described with reference to FIG. 21 which is a flow chart. The power supplies of the film scanner and the external apparatus 2810 are assumed to be turned on to start the firmware and the driver software, and a film is assumed to be inserted in a predetermined position by a user under this condition.
At a step S2901, when the user operates the external apparatus 2810 to give an instruction for preview, the external apparatus 2810 communicates through the driver software with the firmware of the film scanner to send to the film scanner designated information about the kind of film, the reading range (a whole image plane, in this instance) and the reading resolution (low resolution, in this instance). At a step S2902, upon receipt of the designated information, the firmware makes electrical preparation by setting, as designated, information relative to the kind of the film, the reading range and the reading resolution.
At a step S2903, the system controller 2811 reads information from the vertical-scanning position detecting part 2815 and controls the vertical-scanning motor 2813 to move the film to an initial position. At a step S2904, the light source lighting circuit 2816 is instructed to turn on the light source 2801. At a step S2905, the system controller 2811 outputs an instruction for output of timing pulses relative to reading one line, such as pulses for driving the CCD and controlling the address of a RAM.
At a step S2906, the vertical-scanning motor 2813 is driven at a predetermined speed. The digital image processing circuit 2807 is caused to perform an AE (automatic exposure) process on the basis of a signal obtained from the CCD 2804 in such a way as to set an apposite brightness. After the AE process, the vertical-scanning motor 2813 is driven to bring the film back to its datum position. The vertical-scanning motor 2813 is again driven to move the film approximately to its middle position and is then brought to a stop.
A focus adjusting action is next performed by moving the film holder 2802 in the direction of the optical axis. The digital image processing circuit 2807 is caused to sample a high-frequency component of each of signals outputted from all the picture elements of the CCD 2804. The film holder 2802 is fixed in a position where a peak value of the high-frequency component is obtained by the sampling process. Then, the vertical-scanning motor 2813 is again driven to bring the film back to the datum position. The timing pulses related to one line reading are outputted. The image data is read for each line at a predetermined exposure time. After that, the digital image processing circuit 2807 is caused to perform its image processing action. Image data thus obtained is sent to the external apparatus 2810.
At the next step S2907, upon completion of scanning the image reading area or range (the whole image plane, in this case), the system controller 2811 causes the vertical-scanning motor 2813 to bring the film back to the initial position. Then, the light source 2801 is put out. Each of the functions is brought to a stop as soon as all image data are outputted. At a step S2908, the firmware of the system controller 2811 enters a routine of waiting for the next command. At a step S2909, the image data is received by the external apparatus 2810. The external apparatus 2810 then provides the user with a whole image of the film by serially displaying images received.
At a step 82910, the user observes the image data provided for preview and further sets conditions for taking images as desired. The user then gives an instruction for main scanning on the basis of the image capturing conditions thus set. Then, like at the above-stated step S2901, the driver software of the external apparatus 2810 sends the designated information about the kind of the film, the reading area, i.e., a reading range designated by the user, and the reading resolution, i.e., a reading resolution designated by the user, to the firmware of the film scanner. At a step S2911, upon receipt of the information on the reading conditions from the external apparatus 2810, the system controller 2811 executes the actions of the above-stated steps S2902 to S2908 under conditions set for the main scanning.
At a step S2912, the image data sent to the external apparatus 2810 is displayed and is arranged to be storable in a discrete storage medium, such as a hard disk, a magneto-optical disk, a floppy disk or the like.
The conventional film scanner described above, however, necessitates many members to be moved for a focusing action (focus adjustment). These members cause an increase in mechanical load and degrade the quality of images as they prevent attaining an adequate degree of film surface moving precision. Further, in cases where images are to be read through an adapter by transporting a long film which is rolled into a coiled shape, focus must be adjusted by moving, at the same time, the film transport adapter which is heavy. In such a case, the mechanical load further increases.
The conventional film scanner described above has presented another problem. Since the automatic focusing (AF) action is arranged to be carried out by scanning again the film after the same film is scanned once for an automatic exposure (AE) setting action at the time of prescanning and is brought back to the initial position, the images cannot be taken in before completion of these two actions. The arrangement of the conventional film scanner thus requires an excessively long time before the commencement of an actual image scanning operation. The comfort of operational environment thus has been impaired by the long time required for the preliminary actions.
It is an object of the invention to provide an image reading apparatus which is arranged to be capable of stably reading images.
It is another object of the invention to provide an image reading apparatus which is arranged to permit reduction in mechanical load thereon.
It is a further object of the invention to provide an image reading apparatus arranged to permit focus adjustment to be easily accomplished.
To attain the above objects, in accordance with one aspect of the invention, there is provided an image reading apparatus which comprises holding means for holding an original, an image sensor for picking up an image from the original held by the holding means, a lens for forming on the image sensor an image of light having passed through the original, fixing means for keeping a distance between the image sensor and the lens constant, and focus adjusting means for adjusting focus by moving the fixing means with respect to the original.
The above-stated arrangement not only permits reduction of mechanical load imposed on the image reading apparatus but also enables the image reading apparatus to stably read images and to adjust focus without difficulty.